 |
Moteur de recherche de fiches techniques de composants électroniques |
|
|
Moteur de recherche de fiches techniques de composants électroniques |
|
LM317HVH Fiches technique(PDF) 5 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM317HVH Fiches technique(HTML) 5 Page - National Semiconductor (TI) |
|
|
5 / 15 page  Application Hints In operation, the LM117HV develops a nominal 1.25V refer- ence voltage, V REF, between the output and adjustment ter- minal. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I 1 then flows through the output set resistor R2, giv- ing an output voltage of Since the 100 µA current from the adjustment terminal repre- sents an error term, the LM117HV was designed to minimize I ADJ and make it very constant with line and load changes. To do this, all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise. External Capacitors An input bypass capacitor is recommended. A 0.1 µF disc or 1 µF solid tantalum on the input is suitable input bypassing for almost all applications. The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used but the above values will eliminate the possiblity of problems. The adjustment terminal can be bypassed to ground on the LM117HV to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10 µF bypass capacitor 80 dB ripple rejec- tion is obtainable at any output level. Increases over 10 µF do not appreciably improve the ripple rejection at frequen- cies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device. In general, the best type of capacitors to use are solid tanta- lum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25 µF in aluminum electrolytic to equal 1 µF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 µF disc may seem to work better than a 0.1 µF disc as a bypass. Although the LM117HV is stable with no output capacitors, like any feedback circuit, certain values of external capaci- tance can cause excessive ringing. This occurs with values between 500 pF and 5000 pF. A 1 µF solid tantalum (or 25 µF aluminum electrolytic) on the output swamps this effect and insures stability. Any increase of load capacitance larger than 10 µF will merely improve the loop stability and output impedance. Load Regulation The LM117HV is capable of providing extremely good load regulation but a few precautions are needed to obtain maxi- mum performance. The current set resistor connected be- tween the adjustment terminal and the output terminal (usu- ally 240 Ω) should be tied directly to the output of the regulator rather than near the load. This eliminates line drops from appearing effectively in series with the reference and degrading regulation. For example, a 15V regulator with 0.05 Ω resistance between the regulator and load will have a load regulation due to line resistance of 0.05 Ω xI L. If the set resistor is connected near the load the effective line resis- tance will be 0.05 Ω (1 + R2/R1) or in this case, 11.5 times worse. Figure 2 shows the effect of resistance between the regula- tor and 240 Ω set resistor. With the TO-3 package, it is easy to minimize the resistance from the case to the set resistor, by using two separate leads to the case. However, with the TO-5 package, care should be taken to minimize the wire length of the output lead. The ground of R2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation. Protection Diodes When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most 10 µF capacitors have low enough internal series resistance to deliver 20A spikes when shorted. Although the surge is short, there is enough energy to damage parts of the IC. When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regu- lator, and the rate of decrease of V IN. In the LM117HV, this discharge path is through a large junction that is able to sus- tain 15A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 25 µF or less, there is no need to use diodes. The bypass capacitor on the adjustment terminal can dis- charge through a low current junction. Discharge occurs when either the input or output is shorted. Internal to the LM117HV is a 50 Ω resistor which limits the peak discharge current. No protection is needed for output voltages of 25V DS009062-5 FIGURE 1. DS009062-6 FIGURE 2. Regulator with Line Resistance in Output Lead www.national.com 5 |
Numéro de pièce similaire - LM317HVH |
|
Description similaire - LM317HVH |
|
|
|
Lien URL |
| Politique de confidentialité |
| ALLDATASHEET.FR |
| ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
French ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
